1. Field of the Invention
The invention relates to an arrangement having a superconductive cable which consists of a superconductive conductor and a superconductive screen that encloses the latter with the interposition of a dielectric and which is enclosed, with the inclusion of a free space for conveying a refrigerant, by a cryostat which consists of two metal tubes arranged mutually concentrically, between which vacuum insulation is arranged (WO 03/052775 A1).
2. Description of Related Art
A superconductive cable in modern technology has electrical conductors made of a composite material, which contains a ceramic material that enters the superconducting state at sufficiently low temperatures. With sufficient cooling, the electrical DC resistance of a correspondingly constructed conductor is zero so long as a particular current strength is not exceeded. Suitable ceramic materials are for example YBCO (yttrium-barium-copper oxide) or BiSCCO (bismuth-strontium-calcium-copper oxide). Sufficiently low temperatures to bring such a material into the superconductive state lie, for example, between 67 K and 110 K. Suitable refrigerants are for example nitrogen, helium, neon and hydrogen or mixtures of these substances.
In the arrangement according to WO 03/052775 A1, which was mentioned in the introduction, a superconductive cable with a cold dielectric is used. It consists of an inner conductor applied onto a tubular carrier, and a screen arranged concentrically therewith, which are mutually separated and kept at a distance from one another by the dielectric (insulation). The conductor and the screen consist for example of bands of superconductive material, such as YBCO or BiSCCO, which are wound with a long pitch around a support while lying tightly together. This known superconductive cable is constructed so that the superconductive screen externally screens the magnetic field of the superconductive conductor during unperturbed operation. In the event of a short-circuit, the screen changes its impedance so that the magnetic field of the conductor is no longer fully screened. Not only can such a short-circuit therefore lead to destruction of the cable (burn-out), but electromagnetic perturbations can also occur outside the cryostat.